The adipose conversion of susceptible 3T3 cells in culture is a faithful model of fat cell formation in development. This process depends on the presence of an adipogenic factor present in serum and in the pituitary. The adipogenic factor of the pituitary has now been determined to be growth hormone. In simple culture assay, the adipose conversion of 3T3 cells can be made to depend on the presence of growth hormone, which acts as a differentiation hormone. The assay is specific and very sensitive. The specific portion of the growth hormone molecule responsible for this effect will be investigated. In the adipose conversion there take place large changes in the protein composition of the cells, in order to provide the requisite lipogenic and lipolytic enzymes and numerous other proteins that make up the differentiated state of the adipose cell. The altered protein composition is the result of changes in the cellular content of mRNA for each protein. This response is subject to modification by insulin. We plan to study the effect of all agents known to affect adipose conversion with respect to their ability to modify synthesis of specific enzymes and other proteins.